Leveling devices together with measuring rods are used during measurement or leveling. A leveling device comprises a measuring telescope and a device in the form of a spirit level, for example, which ensures the substantially horizontal alignment of the optical axis of the measuring telescope. If the leveling device is mounted on a tripod, then the measurement horizon can be produced using three adjustable foot screws of the tripod by means of the spirit level being leveled. Besides coarse leveling using a box level, it is also possible to carry out fine leveling, wherein a more accurate tubular level, for example, is used. With the aid of a compensator, it is possible to level the target axis of the leveling device even without a precision level. At least part of the residual inclination of the target beam which remains after preliminary leveling using the box level is compensated for by the compensator using the gravitational force. The compensator can attenuate undesirable oscillations with a damping.
When looking through the telescope at the leveling rod, it is possible to determine the perpendicular distance between the rod attachment point and the horizon. Leveling rods have a height of 4 m, for example. An accurate scale is situated at least on a longitudinal region. The zero point of the graduation is the rod attachment point. Various embodiments are known for leveling rods, wherein the latter can have a box level and a handle on the rear side, for example. The rod is kept perpendicular by leveling the spirit level. There are also rods which comprise at least one further graduation.
In combination with digital leveling devices which image the sighted region onto a sensor array and carry out an evaluation of this imaging, corresponding digital leveling rods are used. Such a measuring rod can be automatically read by the device and the data can be evaluated and stored. In order to automate leveling, measuring rods having at least one automatically evaluatable coding are also required—alongside the evaluation and storage elements of the leveling device.
In the case of the known digital leveling devices, the telescope comprises at least one objective, a focusing device, a beam splitter, a cross-line, an eyepiece and a detector comprising the sensor array. With the optical system, a rod can already be read by eye. Since part of the light is deflected in the beam splinter onto a detector for the electronic image conversion, the data can also be detected automatically. The beam splitter can be embodied as a band pass filter e.g. in such a way that spectral ranges of the electromagnetic radiation which are important for the eye are forwarded to the eyepiece and other spectral components are fed to the sensor array.
The measurement sequence is controlled by a processor unit, which not only evaluates the measurement in real time but can also provide corrections dependent on the ambient conditions—for example on temperature—for which purpose various evaluation algorithms are known. Most of these algorithms use a section of the graduation and determine not only the sighted height but also a distance.
The detector converts the received coded pattern of the rod into digital data. Furthermore, the position of the focusing lens is recorded by the focus sensor. The approximate distance between device and rod can be determined from this position. In a distance range of 1.80 m to 100 m, the focusing lens is displaced by approximately 14 mm, for example. In the case of the known solutions, the distance derived from determining the position of the focusing lens is not determined accurately enough. Moreover, the adjustment of the focusing lens is time-consuming.
In the course of measurement using a digital leveling device, in the first step, as in the case of a conventional method, the leveling rod has to be targeted and focused. After the measurement key has been actuated, the position of the focusing lens is registered and the compensator is monitored. In the subsequent step, the target height and the distance are determined approximately. Finally, in the last step, the exact height and the distance are determined by means of evaluation, more particularly correlation, methods. In order to be able to carry out a correlation, it is necessary to store a reference signal corresponding to the imaging of the leveling rod. The height can be determined, for example, by the measurement signal being shifted until reference signal and measurement signal correspond as well as possible. The shift in the measurement signal corresponds to the height sought. Since the measurement signal is imaged at different magnitudes depending on the distance, the scale of the measurement signal has to be matched to the scale of the reference signal beforehand.
Digital leveling devices are known for example from the patent documents DE 36 18 513 C2, DE 198 33 996 C1, EP 1 066 497 B1 and DE 198 04 198 B4, wherein the detectors in the last two documents comprise two-dimensional sensor arrays. EP 0 066 497 B1 describes an evaluation method wherein a slanted position of the measuring rod is determined or compensated for. Moreover, an additional distance measuring device is proposed for accurately determining distance, which increases the device and evaluation outlay. DE 198 04 198 B4 describes embodiments in which the image signals are evaluated by means of Fourier transformations, which improves the correlation with the reference signal of the measuring rod.
EP 0 808 447 describes a device in which the imaging optical unit has a plurality of differently imaging pupil zones, to which spatially resolving optoelectronic detectors or partial regions of a spatially resolving optoelectronic detector are assigned, such that the imaging optical unit enables simultaneous imaging from different distance ranges. The construction of this device is relatively complex and there are distance ranges which are not sharply imaged by any pupil zone.
In the case of the known solutions, providing evaluatable information of a sighted measuring rod independently of the distance thereof from the leveling device is complex. Moreover, when determining the height, it is not possible to correct small deviations from the horizontal alignment of the telescope or of the leveling device with a small outlay.
One problem consists, then, in finding a solution with which evaluatable information of a sighted measuring rod can be provided in a simple manner in a large distance range with respect to the digital leveling device. In particular, the imaging optical unit is intended here to be less susceptible to faults, thereby enabling the height information to be determined more robustly and more precisely.
Moreover, as a further, specific problem, the intention is also to enable exact height values to be determined if small deviations from the horizontal alignment of the leveling device occur.